There are a number of threads on the Mystara message board currently discussing Shadowdeep, it is a work in its inception at the moment - the following are some articles which may not be fully fleshed out yet. The threads thus far include:
Rockhome
Shadowdeep prestige classes
NPCs of the Shadowdeep
Races of the Shadowdeep
Regions of the Shadowdeep
Magic of Annwn
Shadowdeep
The Cavern of Thirith by Rodger Burns, from The Piazza posted 07 June 2009.
Wirrtenheid by Lost Woodrake, from the Mystara Message Board posted 09 June 2004.
Magic of Annwn by Lost Woodrake, from the Mystara Message Board posted 09 June 2004.
NPCs of Annwn by Lost Woodrake, from the Mystara Message Board posted 09 June 2004.
Regions of the Shadowdeep by Andrew Theisen, from the Mystara Message Board posted 08 June 2004.